From now on we have to specify the type of black hole from the point of view of intensity of its rotation. We start from the high end of the \(C\)  range corresponding to the so-called extremal Kerr black hole, when the two horizons coincide: \(C=1\)  and \(r^{extr.}_{{\cal H}}=r_s/2=M\) . Also, we have two different circular photon orbits in the equatorial plane of the Kerr black hole, which are located at [1]}, [2]}
\(r_1=r_s\left[1+\cos \left(\frac{2}{3} \arccos \left(-\frac{|a|}{M}\right)\right)\right],\) 
\(r_2=r_s\left[1+\cos \left(\frac{2}{3} \arccos \left(\frac{|a|}{M}\right)\right)\right].\) 
